Over the years, I have commonly found that about 10-20% of my students have difficulty isolating DNA from their buccal (Cheek) samples. This typically occurs when centrifugation of these isolates (even at very low speed) intended to pellet cells prior to lysis and DNA isolation, results in the immediate lysis of cells and release of DNA into the saline solution. Sometimes this goes without the student noticing or appreciating what is happening in the tube and leads to a failure to obtain any detectable (by UV) or amplifiable (by PCR) DNA in their final tube.
Just today, Dr. Jerry Coyne (Faculty at the University of Chicago, author of ‘Why Evolution is True‘ and host of a blog of the same name), reported that the buccal sample he sent to 23andMe had a similar outcome.
They write to him, “Our laboratory tried to extract DNA from your sample, but unfortunately the concentration wasn’t high enough to meet our standards. While it is uncommon, it does happen occasionally due to biological variability between people.”
I still don’t know why some individuals’ cells appear fragile in this method, but perhaps it’s not entirely unique.